they blame israel for his death. israel denver it. a murder investigation began after a swiss lab found high levels of a lethal radioactive substance, polonium, on his clothing. scientists said they needed to examine his remains to know more. big blue tarps surround arafat's grave kept prying eyes away as workers drilled through layers of concrete to reach the tomb. some supporters were opposed to disturbing the gravesite, others saying it's necessary to learn the truth. this man says, we have to know why he died because he represents the palestinian people and the arab world. experts from switzerland, france and russia will test the sample. it could take months for the results to come back and then even, the mystery may not be resolved. polonium decays quickly. even if he was murdered, it may never be known. rita nissan for cbs news. >>> music and candlelight at san francisco city hall tonight as friends and families remember two slain city leaders. today marks the 34th anniversary of the assassinations of mayor george moscone and su